In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common. The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and alternatively for CO2 sequestration. Many of the world's oil and gas wells produce from unconsolidated sandstones that produce formation sand with reservoir fluids. Problems that are associated with sand production include plugging of perforation tunnels, sanding up of the production interval, accumulation in surface separators, and potential failure of downhole and surface equipment from erosion. Soft formation wells require specialized sand control completion practices to allow hydrocarbons to be produced without formation sand. While it is important to effectively prevent sand production, it is equally important to do so in a way that does not hinder a well's productivity.
A multilateral borehole system includes at least a primary borehole and a lateral borehole extending therefrom. Multilateral boreholes generally require junctions at intersection points where lateral boreholes meet a primary borehole or where lateral boreholes meet (acting then as subprimary boreholes) other lateral boreholes. Multilateral junctions are typically Y-type constructions intended to create flow paths at borehole intersections and are generally referred to as having a primary leg and a lateral leg. The multilateral junction between the primary borehole and the lateral borehole in some cases is an avenue for sand and other particulate matter infiltration into the borehole system, which generally results in the entrainment of such particulate matter with the production fluid. Clearly, it is undesirable to produce particulate matter since those particulates would then need to be removed from the production fluid adding expense and delay to a final release of a product. The reasons for particulate infiltration through a junction in a multilateral borehole are many, including the not entirely controllable window size and shape which is generated by running a milling tool into the primary borehole and into contact with a whipstock, whereafter the mill tool mills a window in the casing of the primary borehole. The milling process itself is not precise and thus it is relatively unlikely that a precise window shape and size can be produced. Lateral liners that are run in the primary borehole to extend through a milled window and into a lateral borehole are constructed with regular patterns and sizes at the surface. When a regular pattern at the top of such a liner is seated against a milled window in the downhole environment, it is relatively unlikely that the liner will seat correctly in all regions of a milled window. This leaves gaps between the liner and the milled casing in the primary borehole resulting in the aforesaid avenue for infiltration of particulate matter to the borehole system.
In order to control sand production in this area, the prior art has proposed employing scaling materials in the area of the multilateral junction, as well as sleeves having a pre-machined window therein to ensure that a liner will seal there against.
The art would be receptive to improved and/or alternative apparatus and methods for reducing the amount of particulate matter infiltrating the wellbore system at a junction in a multilateral wellbore.